/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
 *  with the License.  You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing,
 *  software distributed under the License is distributed on an
 *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *  KIND, either express or implied.  See the License for the
 *  specific language governing permissions and limitations
 *  under the License.
 */
package org.apache.causeway.extensions.sse.applib.annotations;

import org.apache.causeway.extensions.sse.applib.service.SseChannel;

/**
 * Server-sent events.
 *
 * @see <a href="https://www.w3schools.com/html/html5_serversentevents.asp">www.w3schools.com</a>
 *
 * @since 2.0 {@index}
 */
public interface SseSource {

    void run(SseChannel channel);

    String getPayload();

    // -- PROPERTY ANNOTATION DEFAULT

    /**
     * This class is the default for the
     * {@link ServerSentEvents#observe()} annotation attribute.
     */
    public static final class Noop implements SseSource {

        @Override
        public void run(SseChannel channel) {
            // just do nothing
        }

        @Override
        public String getPayload() {
            return "";
        }

    }

    // -- BASIC PREDICATES

    public static boolean isObservable(Class<?> type) {
        if(type==null) {
            return false;
        }
        if(!SseSource.class.isAssignableFrom(type)) {
            return false;
        }
        return !type.equals(Noop.class);
    }

}
